Pulping of lignocellulosic material



w d tes- .other processes.

I 2,939,813 PULPlNG F LIGNOCELLULOS'IC MATERIAL Morris Wayman and Gordon R. Harris, Prince Rupert,

British Columbia, Canada, asslgnors to Columbia Cellulose Company Ltd., Prince Rupert, British Columbia,

Canada, a company of Canada 7 No Drawing. Filed Apr. 25, 1956, Ser. No. 580,472

6 Claims. (Cl. 162-78) -lulosic material which will give a high yield of cellulose requiring little or no further purification.

Another object of this invention is to provide a process" for pulping or bleaching lignocellulosic material with peracetic acid. V

Other objects of this invention will be apparent from the following detailed description and claims. t

According to the present invention, lignocellulosic materials, for example, wood are pulped with peracetic acid to produce a high yield of pulp that has a good white color and is substantially free from lignin. For many purposes,

such as the manufacture of glassine, little or no additional t purification of the said pulp is required because of its good color and high purity. For other purposes, such as the preparation of high quality and special purpose papers ofzwhich photographic paper is an example, it may be necessary to subject the pulp to a mild alkaline extraction with dilute aqueous caustic. In those cases where the specifications which the pulp must meet are quite stringent, as for pulp that is to be used in the manufacture of cellulose derivatives, it may be necessary to extract the pulp with aqueous caustic at elevated temperatures or in several stages in order to obtain a product having the desired properties. It may also be necessary, where pulps' of exceptional brightness are not required. All these treatments subsequent to the pulping step itself may be quite mild as compared with the treatments to which pulp must be subjected when it has been prepared from lignocellulosic materials by conventional pulping processes such as the sulfite process. As a result, the cost or such subsequent treatments is held to a minimum as is the loss in yield and the further degradation of the cellulose molecules.

The pulp produced by the process of this invention beats up very readily so that it may advantageously be employed for the manufacture of parchment and glassine type of papers and will require only a minimum of beating time to prepare it for such use.

Lignocellulosic materials to which the process of this invention is applicable are primarily woods, including softwoods and hardwoods. It may also be applied to the pulping of other lignocellulosic materials such as straws, grasses and the like. In treating woods in accordance with this invention, there may be employed chips of the wood as is the general practice in the pulping of wood by However, it has been found that it is possible to obtain improved results if there are employed thin Waters of wood in which no portion of the wood is more than 0.015 inch from a surface thereof. When such thin wafers are employed, it is possible to complete the pulping of the wood in shorter periods of time, at lower temperatures and with reduced concentrations of reagents process. For example, there may be employed wood that has been defibered by the Asplund process in which wood chips are first heated with steam to an elevated temperature and are then passed between a pair of discs, one stationary and the other rotating where the chips are pro-'. gressively broken to bundles of fibers, individual fibers:

--' and fiber fragments. Other processes that may be employed to defiber the wood include heating the wood in a pressure vessel to very high pressures in the neighborhood of 1000 pounds per square inch gage with steam and then exploding it from the vessel. The defibered wood responds very rapidly to the process ofthis invention so that it is possible to obtain therefrom a highly purified pulp in an extremely short period of time. Surprisingly enough, sawdust is not pulped rapidly with the process of this invention and requires a longer pulping period than wood 1 chips.

The peracetic acid that is employed in carrying out the process of this invention should have a concentration of between about 10 and 40% by weight, calculated before dilution with the moisture contained in the lignocellulosic material. The lower concentrations of peracetic acid areespecially useful in treating wood wafers or defibered wood. The liquid to lignocellulosic material ratio in carrying out theprocess should be between 8:1 and 20:1 calculated on a dry lignocellulosic material basis. The

pulping may be carried out at temperatures between 60 3 C. and the boiling point of the peracetic acid at atmospheric pressure or, preferably, at temperatures between,

60 and C.. One of the advantages of this process is that it may be carried out at atmospheric pressure,

eliminating the need for the heavy, expensive pressure vessels that have previously been employed for the pulping of lignocellulosic materials. However, if desired, the

pulping maybe carried out atsuperatmospheric pressures. The; timehre'quired for the pulping" will depend; on the physical stateof the lignocellulosic material, the results desired andthe precise conditionsemployed during the pulping andrnay range from as little as 6 minutes, or less,

to 360 minutes, or more.

The process of this invention may be carried out on a batch basis. However, because it is possible to effect the pulping at atmospheric pressure and to complete the pulping in relatively short periods of time, this process lends itself especially well to being carried out in a continuous manner. In such case, the lignocellulosic material and the peracetic acid may be mixed in any suitable manner and then caused to move through a reactor for the desired period of time.

When the pulping operation has been completed, the pulp is separated from the liquid and washed. For some purposes, the pulp may be used without further purification or bleaching. For other purposes, as pointed out more fully above, the pulp may be purified, bleached or both purified and bleached to prepare it for further use.

The following examples are given to illustrate this invention further:

Example I Hemlock chips containing 48.5% by weight of moisture Patented June 7, i960 retained on a 0.5 screen. (The screen size is a measure of the diameter of the holes in the screen.) The chips are immersed in aqueous 26% by weight peracetic acid also containing 66% by weight of water plus acetic acid, 5.4 by weight of hydrogen peroxide and 2.5% by weightof sulfuric acid (total active oxygen 8.1%), employing a liquid to chip ratio of 9.8 to 1 (dry wood basis). The charge is brought to 100 C. at atmospheric pressure and held at this temperature for 2 hours. Then, the pulp is washed with water and dried. There isobtained a 44% by weight yield of a pulp having a good white color. The pulp. has a viscosity in cupriethylenediamine of 20 (TAPPI T230), a permanganate number of 1.7 andan alpha cellulose content of 56% EJ cample II Hemlock wafers 0.02 to 0.03'inch thick and containing 41.9% by weight of moisture are immersed in aqueous 39% by weight peracetic acidalso containing 34% by' Example III Asplund fibers containing 66.0% by weight of moisture prepared from Douglas fir chips are immersed in aqueous 25% by weight peracetic acid also containing 64% by weight of acetic acid plus water, 2.5% by weight of sulfuric acid, 8.3% by weight of hydrogen peroxide '(total active oxygen 9.2%), employing a liquid to fiber ratio of 19.4 to 1 (dry wood basis). The charge is brought to 60 C. and held at this temperature under atmospheric pres sure for 30 minutes, washed with water and dried. There is obtained a 56% by weight yield of a pulp having a good white color. The pulp has a viscosity in cupriethylenediamine of 5, a permanganate number of 2.6 and an alpha cellulose content of 61.1%.

- Example IV Hemlock chips containing 42.5% by moisture, and screened as described in Example I are immersedin aqueous' acetic acid, water, sulfuric acid, and hydrogen peroxide to giye peracetic acid containing 8.8% total active oxygen employing a liquid to chip ratio of '16 to 1 (dry wood basis). The chips are digested for 4 hours under factor of\54.1, a tear factor of 65.8 and a folding en- 4 atmospheric pressure at a temperature between and C., washed with water and dried. There is obtained a 50. 6% by weight yield of a pulp having a good white color. The pulp has a viscosity in cupriethylenediamine of 23, a permanganate number of 1.1 and an alpha cellulose content of 60.7%. 1:

The pulp, Without further treatment, ,hasa Canadian Freenes'sof 505. When'fo'rmed into a sheet it has a burst durance oflOS. v v

It is to be understood that the foregoing detailed description is merely given byway of illustration and that many variations maybe made therein without departing from the spirit of out-invention.

Having described our invention, what we desire to secure by Letters Patent is:

1. Process which comprises pulping wood particles selectedfrom the group consisting ,of wood wafers in which no portion of the wood is more than 0.015, inch.

from a surface thereof anddefibered woodwith pe'racetic acid having a concentration of between about 10 and 40% by weight. V V 1 ,2. Process which comprises pulping wood-wafers in which no portion of the wood'is more than 0.015 inch from a surface thereof with peracetic acid having a con-.

centration of between about 10 and 40!% byweightat a temperature of between about 60 and 100 C...

v 3. Process which comprises pulping defibered wood, with peracetic acid having a concentration or between about 10 and 40% by weight at a temperature of between about 60 and 100 C., v

4. Process which comprises pulping wood with peracetic acid having a concentration of between about .10 and 40% by weight at a temperature of between about 60' and 100 C. employing a liquid to Wood ratio of between 1 8m 1 and 20 to 1.

5. Process which comprises pulping wood waters in V which no portion ofthe wood is morethan 0.015 inch from a surface thereof with peracetic acid having a corn centration of between about 1 0 and 40% by weight at a temperature of between about 60 and 100 C. employing a liquid towood ratio of between 8 to land 20 to l.

6. Process which comprises pulping defibered wood; with peracetic acid having a concentration of between about 10 and 40% by weight at a temperature of be tween about '60 and 100 C. employing a liquid to wood ratio of between 8 to 1 and 20 to 1.

,- References Cited in the file of this patent V UNITED STATES PATENTS 2,394,939 2,511,096

Dreyfus Feb. '119, 1946 Bate June 13,1950 

1. PROCESS WHICH COMPRISES PULPING WOOD PARTICLES SELECTED FROM THE GROUP CONSISTING OF WOOD WAFERS IN WHCH NO PORTION OF THE WOOD IS MORE THAN 0.015 INCH FROM A SURFACE THEREOF AND DEFIBERED WOOD WITH PERACETIC ACID HAVING A CONCENTRACTION OF BETWEEN ABOUT 10 AND 40% BY WEIGHT. 